Hi Keith,
I highly recommend you to buy the special issue of Le Règne Minéral about Chessy mines.
It is available there:
[
www.minerauxetfossiles.com]
You have to scroll down to find it.
Older but always so accurate for such French famous locality, you have:
Lacroix, A. (1893): Minéralogie de la France et des ses colonies, Paris. 5 volumes: vol. 1 (1893-95); vol. 2 (1897); vol. 3 (1901); vol. 4 (1910); vol. 5 (1913).
If you want, I could make a pdf of the cuprite pages for you, just tell me by PM.
Amicalement.
Jean-Marc